Abstract

The diffusion coefficients of simple chain models are analyzed as a function of packing fraction, η, and as a function of a parameter C that is the density raised to a power divided by temperature to look at scalar metrics to find master curves. The central feature in the analysis is the mapping onto an effective hard site diameter, d. For the molecular models lacking restrictions on dihedral angle (e.g., freely jointed), simple mappings of molecular potential to d work very well, and the reduced diffusion coefficient, D*, collapses into a single-valued function of η. Although this does not work for the dihedral angle restriction case, assuming that d is inversely proportional to temperature to a power results in collapse behavior for an empirically selected value of the power. This is equivalent to D* being a single-valued function of C. The diffusion coefficient of a single-site penetrant in the chain systems also is found to be a scalar metric that can reduce the chain diffusion data for a given system to a single master curve.

Received 06 August 2013Accepted 03 December 2013Published online 27 December 2013

Acknowledgments:

The authors thank Douglas Adolf, who was working at Sandia National Laboratories (Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.) during the time this research was performed, for many useful discussions and funding. This research was performed at the New Mexico Institute of Mining and Technology.